The present invention regards an acoustic concentrator system and method for capturing particulates entrained in gaseous (e.g., aerosol) or liquid fluids, and delivering a concentrated sample or stream of the particulate. In some embodiments the system and method can further provide a continuous flow of concentrated particulate. By concentrating the particulate entrained in gaseous or liquid fluids, the system of the present invention can be used to more effectively and accurately sample fluids for particulates.
Prior art related to aerosol concentration relies on inertial methods of particle separation and concentration within, typically, an air stream. Specifically, when an air stream containing particulate undergoes acceleration, the relatively high inertia of the particulate (as compared to the surrounding air) causes relative motion between the air and particulate, allowing the particulate to be separated from the air. For example, a virtual slit impactor is a well-known aerosol concentrator that concentrates particulate by extracting a minor flow that contains more particulate through a narrow aperture or slit, while the major flow containing less particulate is drawn through a 90-degree turn in the housing (the inertia of the particulate makes it difficult to continue through the turn). However, high humidity (>90%) air can cause condensation and accumulation of particulate on internal surfaces (e.g., precisely machined knife edges for diverting major and minor air flows), which negatively impacts the concentration of particulate delivered by the system. Furthermore, the inertia methods are less effective as the size of the particulate decreases (e.g., below 3 microns).
In contrast to the prior art, the present invention uses a fundamentally different approach to particulate concentration, exploiting the physical interaction between a sound field and a particulate. In the system and method of the present invention, the sound field is used to force particulates entrained in a fluid towards storage locations near or within nodal and anti-nodal positions within an acoustic resonator. When the sound field is activated at a sufficiently high sound pressure level, the acoustic force overcomes other forces experienced by particulate, e.g., air flow and viscous drag. Particulates are thereby trapped in storage locations of the resonator. When the sound field is deactivated, the particulate is released from the storage locations and is delivered by the system of the present invention as a concentrated stream of particulate.
The present invention is thereby a novel improvement over prior art systems. As hereinafter discussed, the invention expands the application methods to include particulate concentration in fluids, improves concentration of particulates below 3 micron, provides a more compact system, allowing for adjustability of the level of concentration, functions over a wide range of humidity and temperature (as the system does not provide machined knife edges that may accumulate particulates in high humidity), and consumes less overall power than the prior art systems.
Useful applications of the system and method of the present invention include integration into the inlet of an aerosol detection system, whereby the present invention increases the sensitivity of the detection system by concentrating particulates within the sampled air, leading to earlier detection of aerosol agents. Other applications include improving the sensitivity of other biological, chemical, radionuclide, and explosives sensors, by delivering a more effective sample of particulates entrained in a fluid. Similarly, the system and methods of the present invention may be used to process powdered materials, such as in the manufacturing of pharmaceutical powders.